Studies: Suicides linked to sunshine

Scripps Howard

Can too much sunlight make people more inclined to take their own lives?

It seems counterintuitive to those who have endured long, dreary winters that late spring and early summer are the height of suicide season in higher latitudes, including the United States.

But two studies from opposite ends of the world and six years apart seem to support the notion that longer days and more exposure to sunshine play a role in suicide rates.

A 2003 Australian study found that, over a 10-year period, the rate of suicide peaked in spring and summer in the state of Victoria and fell to the lowest level in winter.

And in a new study published online Friday, a team of Scandinavian scientists found that suicide rates in Greenland increase during the summer, peaking in June.

The leaders of both studies suspect that sunlight is the key factor, although for slightly different reasons.

For the Greenland study, published by BMC Psychiatry, Karin Sparring Bjorksten of the Karolinska Institute in Sweden and her colleagues looked at all suicides in the country between 1968 and 2002. The seasonal pattern was consistent and particularly notable in the northern part of the country.

“In terms of seasonal light variation, Greenland is the most extreme human habitat. We found that suicides were almost exclusively violent and increased during periods of constant day. In the north of the country, 82 percent of the suicides occurred during the daylight months,” Bjorksten said.

Bjorksten speculates that insomnia caused by incessant daylight may be at least partly to blame. It may also be that constant daylight generates imbalances in the brain chemical serotonin, with spikes that lead to increased impulsiveness and even further disrupted sleep patterns.

“Light is just one of many factors in the complex tragedy of suicide, but this study shows there is a possible relationship between the two.”

Except for parts of Alaska, there is no constant daylight in the summer for the United States, but suicide rates are consistently highest between May and July, a Scripps review of national suicide statistics for the two most recent years available, 2005-06, showed. Contrary to popular belief, December, with the shortest days and presumed holiday-related stress and depression for many, is the month with the lowest suicide rate.

In the earlier study, Australian researchers under Dr. Gavin Lambert of the Baker Heart Research Institute in Melbourne were actually trying to see if weather conditions affected suicide rates. But they found that temperature or rainfall made no difference, just the average hours of daylight.